Learning and memory during aggression in Drosophila: handling affects aggression and the formation of a "loser" effect.

Aggressive behavior in Drosophila melanogaster serves to acquire or defense vital resources such as food, territory or access to mates. Flies learn from previous fighting experience and modify and adapt their behavior to new situations, suggesting that learning and memory play a major role in agonistic encounters. Prior fighting experience influences the outcome of later contests: losing a fight increases the probability of losing second contests, revealing the formation of a "loser" effect. In a recent publication, we developed a new behavioral arena that eliminates handling of flies prior to, during and after fights to study the learning and memory associated with aggression. We compared two handling procedures commonly used in laboratories to study aggression with the new chambers and demonstrated that handling negatively influences aggression and prevents "loser" effect formation. In addition, we observed new aspects of behavior such as the formation of robust winner effects.